Increasing immuno-virological and biochemical evidence supports the concept that the Epstein-Barr virus (EBV) is the major contributing factor in the multifactorial etiology of nasopharyngeal carcinoma (NPC) and Burkitt's lymphoma. The other contributing factors, such as chemicals, immunosuppressants, and genetic predisposition, interacting with the EBV, undoubtedly play a profoundly important role in induction of these cancers. Moreover, Herpesvirus saimiri (HVS) of the squirrel monkey, and Herpesvirus ateles (HVA) of the spider monkey are prevalent and widely distributed in these monkeys and are known to induce tumors in a variety of nonhuman primates as a result of inoculation of virus or by horizontal spread of virus. For all of these reasons, the cellular and humoral responses of animals bearing these virus-induced tumors are important models for application to diagnosis, prognosis, evaluation of antiviral anticancer drugs and antitumor vaccine preparations in relation to EBV virus activity in humans.